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184 Algae: Anatomy, Biochemistry, and Biotechnology

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pigment concentration C (mol l ), the path length l (cm) and the molar extinction coefficient 1 l ,
which is substance-specific and a function of the wavelength.

I I
A l ¼ log ¼ 1 l Cl (5:1)
I T
Table 5.1 shows the comparison between transmitted light and absorbance values.

INTERFERENCE
Electromagnetic waves can superimpose. Scattered waves, which usually have the same frequency,
are particularly susceptible to the phenomenon of interference, in which waves can add construc-
tively or destructively. When two waves, vibrating in the same plane, meet and the crests of one
wave coincide, with the crests of the other wave, that is, they are in phase, then constructive inter-
ference occurs. Therefore, the amplitude of the wave has been increased and this results in the light
appearing brighter. If the two waves are out of phase, that is, if the crests of one wave encounter the
troughs of the other, then destructive interference occurs. The two waves cancel out each other,
resulting in a dark area (Figure 5.4). The interference of scattered waves gives rise to reflection,
refraction, diffusion, and diffraction phenomena.

REFLECTION
Reflection results when light is scattered in the direction opposite to that of incident light. Light
reflecting off a polished or mirrored flat surface obeys the law of reflection: the angle between
the incident ray and the normal to the surface (u I ) is equal to the angle between the reflected ray
and the normal (u R ). This kind of reflection is termed specular reflection. Most hard polished
(shiny) surfaces are primarily specular in nature. Even transparent glass specularly reflects a
portion of incoming light. Diffuse reflection is typical of particulate substances like powders. If
you shine a light on baking flour, for example, you will not see a directionally shiny component.
The powder will appear uniformly bright from every direction. Many reflections are a combination
of both diffuse and specular components, and are termed spread (Figure 5.5), such as that performed
by Emiliana blooms.

TABLE 5.1
Relationship between Transmitted Light
Percentage and Absorbance Value
Transmittance Absorbance

100 0.000
90 0.045
80 0.096
70 0.154
60 0.221
50 0.301
40 0.397
30 0.522
20 0.698
10 1.000
1 2.000
0.1 3.000